Cells for the electrolysis of alkali salt solutions



April 24, l951 c. DE PREz ETAL 2,550,231

CELLS FOR THE ELECTROLYSIS 0F ALKALI SALT SOLUTIONS Filed MatQh 5, 1947 IN VEN TORS C/mmfs 05,3952 /r/vo BY A L fx/5 54 sm EWS/0 Patented Apr. 24, V1951 CELLS FOR THE ELECTROLYSIS F ALKALI SALT SOLUTIONS Charles De Prez, Uccle-Brussels,

and Alexis Basilewsky, Bortsfort-Brussels, Belgium, assignors to Solvay & Cie, Ixelles-Brussels, Belgium, a Belgian company Application March 5, 1947, Serial No. 732,570 In Belgium March 11, 1946 1 Claim.` (Cl. 204-219) The consumption of electric energy in an electrolytic cell is a function of the ohmic resistance of the apparatus, and it depends mainly on the width of the anode-cathode gap. It vhas always been endeavoured to reduce this gap to a minimum compatible with safe operation, the best results, in apparatus for the electrolysis of salts, being obtained with cells having an amalgamated bottom.

Modern apparatus operate at relatively high temperatures; they are subject to appreciable deformation which renders impossible an accurate adjustment of the anode-cathode gap. It has been proposed to interpose between the i fixed insulating supports and the body of the cell movable rollers permitting free movement of the longitudinally expanding parts. This arrangement, which is based on the old conception `of spaced insulating supports, only confers to the conducting bottom a truly plane surface when it is made of heavy materials capable of rendering it so rigid that bending between the supports is negligible. This solution is acceptable at ordinary temperature, but underI the action of heat, mechanical stresses and deformations arise on accountof the very ibulk of the structure in which uneven expansion stresses take place. Lt is therefore necessary to providea safety margin in the adjustment of the anode-cathode gap. It must also be` kept in mind that phenomena of caustic brittleness are magnied by mechanical stresses.

Moreover an accurate adjustment of the anode-cathode gap is efcient only when the cell cover or slab, which supports the anode, is kept at a fixed distance from the flat conducting bottom or sole. This, however, is not the case in known types of apparatus. Fluid-tightness of the cell is ensured by the insertion of a plastic or elastic packing between the vertical Walls of the trough and the slabs and it follows that both the height of the slabs and their parallelism with the cathode sole depend on the thickness of the packing, which is liable to vary .for different reasons (swelling due to corrosion,

a strong frame which confers the required rigidity to the structure, while the other part forms the electrolysis trough or vat proper, which is of lighter and relatively flexible construction and rests on the rigid frame with interposition of a layer of a thermally and electrically insulating material. Thanks to the light Construction of the electrolysis trough internal mechanical stresses are reduced to a minimum and local distortions are practically avoided; the relatively exible trough is supported over its whole length on the rigid frame and thus takes up its rectilinear shape. The thermal insulation provided by the intermediate layer opposes the transmission of heat to the supporting frame so that the latter remains at a temperature near normal and is not stressed or exposed'to distortion.

In order to keep up the accurate adjustment made possible by the absence of distortion, the cover plates of the cell are directly supported on the vertical Walls of the trough and the requisite fluid-tightness is secured by packing arranged outside and pressed b y a clamp.

In the accompanying drawing diagrammatically illustrating by way of exampleV anelectrolytic cell in accordance with our invention,

Figs. 1 and 2 respectively show the cell in end and side elevation,

Fig. 3 is a longitudinal part sectional elevation on a larger scale and Fig. 4 is a part crosssection.

In the drawing, a is the trough of the electric cell which rests, through the intermediary of an insulating layer b, for example of fibrocement, on a frame c supported on insulators d.

The trough a has a flat sheet iron bottom e, which forms the cathodic conducting sole of the apparatus. The vertical Walls j are covered inwardly with an insulating protecting coating g for example of ebonite or of synthetic resin, and are tightly'secured to the edges of the bottom e, the coating g serving as gasket material between the bottom e and walls f.

In contradistinction to the usual cell construction, the side walls and bottom form a structure free from any strengthening ribs or other reinforcements adapted to making same rigid. The trough is relatively flexible, i. e. it is sufficiently flexible to be stretched flat on the rigid underlying support and to undergo without any warping or buckling the variations in length due to temperature variations.

The insulating layer b comprises in the example illustrated two side strips b, interposed between the trough a and the frame c and a wide center strip b2 forming a heat-protecting screen resting on cross-members h secured to the supporting frame c Preferably the,l trough a is secured at one point to the frame c so that in operation, after successive stoppages and starts, it will always come back to its initial position without having been subjected to prejudicial stresses. VFor thatjpurpose it may be secured to one end of the frame, for instance by means of bolts z' extending through the wings of the ironsforming the walls of the trough and frame.

This construction permits of obtaining a plane sole adapted to keep its shape whatever be the 4 temperature conditions in operation;'thisdbeing a primary requirement for an elective'and-accurate adjustment of the anode-cathodefgap to-.a minimum distance. necessity of maintaining constant the distance resulting from the adjustment.

To meet this further requirement, we support the cover plates i carrying the anodes lc, directly on the Vertical walls j of the trough a, as distinguished from the usual practice, when the said plates rest on a compressible packing. Thus, the distance H between the plates j and the at sole e remains strictly constant and the vertical adjustment of the anodes can be eiected with the greatest accuracy, without any risk of further play.

Fluid-tightness of the cell is ensured by a packing Z arranged outside the trough in a V-shaped groove between the shaped wall f and the edge of the cover plate or plates i. The packing is tightened by a clamping member pressed by any suitable means and guided for example by the interengagement of lugs provided on the cover plates or on the walls, Aand notchesl provided in the members m.

Electric connections between successive cells are provided bybars n secured to the conducting soles of the cells. To that endl the sole e Vmay advantageously beshaped so that it projects `lat-v erally (Fig. 4), beyond the Vertical wall f, the con- Another requirement is the a rigid, metallic, self-sustaining frame structure resting on said insulating supports, said frame structure being formed from elongated side portions and connecting transverse portions, said sideportions l.and said transverse portions defining a substantially planar supporting surface, an elongated electrolysis trough supported on said lframe, said electrolysis trough having a length substantially greater than its width, being substantially more flexible than said frame and comprising a nat sole portion and vertical side Walls and end walls removably secured to said soleportion, gasket material between the sole `portion and the lower surface of the end walls and side walls, a layer of thermal insulating .-materialinterposed between said frame and said Ysole-portion to prevent transmission of heat from -said trough to said frame, and securing means REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES VPA".["EN'2['S Number Name Date 708,796 Clark Sept. 9, 1902 1,227,706 Vaygouny May 29, 1917 1,575,627 Heinze Man-9, 1926 1,942,881 Roth Jan. 9, 1934 2,334,354 Richardson Nov. 16, 1943 2,428,584 Richardson Oct. 7, 1947 2,467,892 Horst Apr. 19, 1949 2,502,888 Ravenscroft Apr.r 4, 1950 FOREIGN PATENTS Number Country Date 316,694 Great Britain Aug. 8,-1929 

